The process of popping corn involves applying heat to convert water in the interior of a corn kernel into steam. Raw corn kernels and cooking oil are placed in a popcorn kettle of a popcorn machine and heated. When the corn kernels reach a sufficiently hot temperature, they can explode due to a high internal pressure caused by transformation of the interior water into steam. These explosions can be violent and can propel popped kernels, raw kernels, and residual oil upward. A significant amount of steam may be generated as well as the interior water makes up approximately 1/7 of the weight of raw corn kernels.
The kettle can include a cover that confines the popped corn, unpopped kernels, oil, and steam in the kettle until a layer of popped corn accumulates. After sufficient accumulation of the popped corn, the cover may be lifted by manual or automatic mechanical means, allowing the popped corn to collect in a cabinet in which the kettle is contained. The lifting of the cover also allows the steam and the oil vapor to rise above a bed of the popped corn in the kettle and escape into the adjacent space in the popcorn machine.